Previous randomized-controlled trials have shown that a peer learning group intervention for career preparation can have positive effects on adolescent career management and the transition to post-comprehensive education in secondary schools. However, this earlier evidence of efficacy has been found by intervention studies that have implemented the method intensively. Earlier studies suggest that tailoring implementation strategies to fit organizational processes may offer opportunities to improve the sustainability and scalability of evidence-based practices. In this study, the implementation of the career preparation intervention was integrated into the school curriculum as a part of regular career counselling, lengthening the delivery timeframe of the intervention programme and using the schools' own guidance counsellors as intervention providers. We conducted a conceptual replication study to investigate how effectively the adapted intervention programme enhanced perceived career preparation skills by carrying out a new cluster randomized-controlled trial among 1068 pupils. Linear mixed models showed that the effect of peer learning sessions on career choice preparedness was positive in comparison to that in the control group. The result suggests that the adapted intervention programme preserved its identifiable positive effects, although dismissing intensive delivery features somewhat reduced the effect size. These study results have implications for school-based career counselling interventions as schools seek to identify evidence-based methods that are cost-efficient and may be integrated into regular school routines.